1. Field of the Invention
The present invention relates to a lens barrel suitable for use in driving in and out in a sink barrel type camera, zoom-driving a photographing lens system in a zooming camera or focus-driving a photographing lens system in an AF camera.
2. Related Background Art
In a recent compact camera, a sink barrel type in which a lens barrel is driven into a camera body is adopted to meet a requirement of compactness and thinness.
In a lens barrel of such a sink barrel type camera, a rotating drive force from a drive source such as an electric motor is transmitted by a drive gear to a rotary cylinder which is rotatably held by a helicoid coupling in a stationary cylinder on a camera body, and the rotary cylinder is driven out along an optical axis while it is rotated so that the lens barrel is projected from the front surface of the camera body to be ready for photographing, and the rotary cylinder is reversely rotated to drive it into the camera body.
In a recent camera, as a part of multi-functioning of the camera, a zoom lens which permits photographing from telescopic range to wide angle range has been used.
In a lens barrel of such a zooming camera, the rotary cylinder is moved back and fourth along the optical axis while it is rotated as it is in the sink barrel type, and a focal distance of the photographing lens held and arranged in the lens barrel in the rotary cylinder is varied in accordance with the drive distance so that the photographing at a desired magnification is attained.
Recently, a combination of the zoom lens and the sink barrel type has been adopted. In such a combination of the zoom lens and the sink barrel type, it is required to increase the rotation angle and the drive distance of the rotary cylinder in the lens barrel and the drive distance of the lens barrel.
Further, auto-focusing (AF) which automatically focuses the lens has been widely adopted. In this case, again, the rotation and the drive of the rotary cylinder in the lens barrel and the drive of the lens barrel are done under a predetermined condition by the transmission of the rotating drive force from an electric motor to focus the lens system.
In the sink barrel type, the zoom type and the AF type, a rotation transmission unit of a drive gear which imparts a rotating drive force from the electric motor to the rotary cylinder usually uses a construction as disclosed in Japanese Laid-Open Utility Model Application No. 2-10514, in which a helical gear is provided on an outer periphery of the rotary cylinder and a stationary cylinder or a drive gear provided on a camera body is meshed therewith, and both cylinders are helicoid-coupled while the rotary cylinder is rotatably driven in the stationary cylinder so that the rotary cylinder is driven out and in along the optical axis.
However, in the prior art construction described above, in order to increase the drive stroke of the rotary cylinder, it is necessary to form the helical gear in a certain range along the optical axis on the outer periphery of the rotary cylinder because there is only one drive gear on the stationary cylinder. In addition, since the rotary cylinder is gradually driven out of the lens barrel so that an end thereof is exposed externally to form an externally viewable part, it is necessary to form an externally viewable part in addition to the gear formation part.
Accordingly, the larger the drive stroke is, the longer is the length of the rotary cylinder along the optical axis. This leads to the increase of the size of the lens barrel and hence the entire camera.